1. Field of the Invention
This invention relates to air conditioning systems and heat pumps. More particularly, this invention relates to an apparatus and method for precooling and subcooling the refrigerant which is condensed by the condenser of the air conditioning system or heat pump operating in a cooling mode. Additionally, this invention relates to an apparatus and method for post heating and subcooling the refrigerant which is evaporated by the evaporator of a heat pump operating in a heating mode.
2. Description of the Prior Art
Presently there exists many types of apparati designed to operate in a thermal transfer cycle to remove heat from one heat sink region and transfer such heat to a different heat sink region. Such apparati include reverse cycle heat pumps and vapor-compression refrigeration systems such as air conditioners, refrigerators, freezers and coolers.
The operation of the thermal transfer cycle of each of the above apparati can be briefly summarized in relation to the various components thereof. More particularly, the thermal transfer cycle is customarily accomplished by a compressor, condenser, throttling device, and evaporator connected in serial fluid communication with one another. The system is charged with a refrigerant which circulates through each of the components to remove heat from the evaporator and transfer such heat to the condenser. During operation, the compressor compresses the refrigerant from a saturated-vapor state to a super-heated vapor state thereby increasing the temperature, enthalpy, and pressure of the refrigerant. The refrigerant then flows through the condenser which condenses the refrigerant at a substantially constant pressure to a saturated-liquid state. The throttling device reduces the pressure of the refrigerant thereby causing the refrigerant to change to a mixed liquid-vapor state. The refrigerant then flows through the evaporator which causes the refrigerant to return at a constant pressure to its saturated-vapor state thereby completing the thermal transfer cycle.
In a refrigerating mode, it is readily apparent that the condenser plays a major role in the refrigerating effect of the thermal transfer cycle. The most common type of condenser presently in use for domestic systems is commonly referred to as an "air-cooled condenser". Such air-cooled condensers typically operate by subjecting the condenser to a flow of free air which absorbs the heat being discharged by the condenser. The advantages of such air condensers include the low cost of moving the free air by means of fans powered by electric motors, the availability of air, and the ease of discharging the heat laden air. The disadvantages of such air condensers is the need for an extremely large heat exchange surface area of the condenser to effect the heat exchanging relationship between the refrigerant passing through the condenser and the flow of free air, the relatively high head pressure involved on the compressor, the fluctuating humidity and temperature of the air, and the lack of any significant subcooling of the liquid refrigerant flowing from the condenser of standard operating conditions. Because of such problems, the air-type condensers are used in conjunction with relatively small refrigeration systems such as those commonly used for domestic purposes.
The second most prevalent type of condenser is what is commonly referred to as a water-cooled condenser in which water is circulated about the condenser to absorb the latent heat of condensation of the refrigerant as the refrigerant is condensed within the condenser. The advantages of such water cooled condensers is the fact that the condenser drops the head pressure off the compressor very rapidly, thereby reducing the pressure differential across the compressor. The amount of electric current required to power the compressor is therefore substantially reduced. Moreover, water-cooled condensers cool the refrigerant by as much as 30.degree. F. or more over an air-cooled condenser. Such subcooling increases the refrigerating effect of the refrigeration cycle by 18 percent to 37 percent or more. Unfortunately, the primary disadvantage of a water cooled condenser is the need for a great volume of water (approximately 2 gallons per minute per tonnage of cooling capacity as recommended by most manufacturers). Additionally, problems exist in discharging the heated water to the environment. For these reasons, water cooled condensers are typically found only on commercial refrigeration systems having cooling capacities greater than 3 tons (12,000 British Thermal Units per hour).
In order to reduce the volume of water discharged in a water-cooled condenser, various water tower condensers have been designed. Typical water tower condensers comprise a reservoir of water which is pumped through a water/refrigerant heat exchanger. The water absorbs heat of condensation of the refrigerant. The absorbed heat in the water is then rejected into the atmosphere by evaporation of some of the water, with the heat evaporazation of the water being used to cool the remaining water. It is noted that due to the evaporation of water, a supply of water must be continually fed to the reservoir to maintain the reservoir at a proper water level. The equilibrium water temperature attainable is equal to the ambient wet bulb temperature. This causes similar problems as noted on air-cooled condensers, because as ambient wet bulb temperature increases, the efficiency of the condenser decreases.
Therefore, it is an object of this invention to provide an apparatus and method which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement which is a significant contribution to the advancement of the thermal cycle transfer art.
Another object of this invention is to provide an apparatus and method which utilizes the advantages of an air-cooled condenser and a water-cooled condenser while eliminating the disadvantages of such condensers.
Another object of this invention is to provide an apparatus and method for precooling the refrigerant prior to the refrigerant flowing into the condenser when the system is operating in a cooling mode.
Another object of this invention is to provide an apparatus and method for subcooling the refrigerant flowing from the condenser when the system is operating in a cooling mode.
Another object of this invention is to provide an apparatus and method for subcooling the refrigerant flowing into the evaporator when the system is operating in a heating mode.
Another object of this invention is to provide an apparatus and method for post heating the refrigerant flowing from the evaporator when the system is operating in a heating mode.
Another object of this invention is to provide an apparatus and method to prevent damage to a compressor due to excessive subcooling when the heat pump is operated in a cooling mode at extremely low outside temperatures.
Another object of this invention is to provide an apparatus and method to prevent damage to a compressor when operating the heat pump in a cooling mode at elevated outside air temperatures.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.